When I speak of a significant portion of hackers, I am not speaking of any particular one. I am not surprised that you'd have learned the formal definition.
Although I have to disagree on how extreme your dismissal is. Absolutely big-O is useful as a starting point and means of informal discussion. However it also provides a framework for how to think about performance, and that can go a lot farther. Being aware of big-O has helped me predict how well real systems will scale, understand bottlenecks, and multiple times has given me a sense as to whether a given implementation's performance is reasonable, or whether a performance mistake needs to be tracked down.